This invention relates in general to electroformed belts, and in particular, to a process for electroforming metal belts.
Electroforming has been known for many years as a method for producing metal objects. In the electroforming process, an electric current is passed through an electrolyte solution in which tare immersed an anode and a cathode. A metal in the electrolyte solution is deposited onto either the anode or the cathode, thus forming an object.
U.S. Pat. No. 3,844,906 to Bailey et al discloses a process for maintaining a continuous and stable aqueous nickel sulfamate electroforming solution adapted to form a relatively thin, ductile, seamless nickel belt by electrolytically depositing nickel from the solution onto a support mandrel and thereafter recovering the nickel belt by cooling the nickel coated mandrel, and effecting a parting of the nickel belt from the mandrel due to different respective coefficients of thermal expansion comprising: establishing an electroforming zone comprising a nickel anode and a cathode comprising a support mandrel, an anode and a cathode being separated by a nickel sulfamate solution maintained at a temperature of about 140.degree. to 160.degree. F. and having a current density therein ranging from about 200 to about 500 amps/ft.sup.2 ; imparting sufficient agitation to this solution to continuously expose the cathode to fresh solution; maintaining the solution within the zone at a stable equilibrium composition comprising nickel, halide and boric acid; electrolytically removing metallic and organic impurities from the solution upon removal from the electroforming zone; continuously charging to the solution about 1.0 to 2.0.times.10.sup. -4 moles of a stress reducing agent per mole of nickel electrolytically deposited from the solution; passing the solution through a filtering zone to remove any solid impurities therefrom; cooling the solution sufficiently to maintain the temperature within the electroforming zone upon recycle thereto to about 140.degree. to 160.degree. F. at the current density in the electroforming zone; and recycling the solution to the electroforming zone.
U.S. Pat. No. 4,501,646 to Herbert discloses an electroforming process for forming hollow articles having a small cross-sectional area. In this patent, the electroforming process employs a cathode for the core mandrel having an electrically conductive, adhesive outer surface, an anode, and an electrolyte bath comprising a salt solution of the metals used for the electrodes. This process utilizes the differences in coefficient of expansion between the mandrel and the electroformed metal to remove the object. Thus, any suitable metal capable of being deposited by electroforming and having a coefficient of expansion between 6.times.10.sup.-6 in /in./.degree. F. and about 10.times.10.sup.-6 in./in./.degree. F. may be used in the process. The disclosed process is used for forming a belt having a thickness of at least about 30.ANG. and stress-strain hysteresis of at least about 0.00015 in/in, and wherein a stress of between about 40,000 psi and about 80,000 psi is imparted to the cooled coating to permanently deform the coating and to render the length of the inner perimeter of the coating incapable of contracting to less than 0.04% greater than the length of the outer perimeter of the core mandrel after cooling.
U.S. Pat. No. 4,664,758 to Grey discloses an electroforming process with an additional step for facilitating the removal process. An electroforming mandrel is provided to which is initially applied, prior to electroforming, a uniform coating of an electrically conductive substrate or metal alloy. The metal or metal alloy has a melting point and a surface tension less than the melting point and surface tension of the mandrel core. The coated mandrel core is immersed in an electroforming bath, and an electroformed metal layer is deposited on the coating, the electroformed metal layer having a melting point greater than the metal or metal alloy. The electroformed metal layer is removed from the mandrel core, thus permitting the mandrel to be reused. This method provides precise control of the electroformed coatings, by compensating for surface defects in the mandrel with this initial coating. Other methods described in U.S. Pat. No. 4,664,758 employ wax or an oxide film as parting aid on the surface of a metal die.
U.S. Pat. No. 4,787,961 to Rush discloses the use of an electroforming process for preparing a multilayered metal belt. A tensile band set is formed from a plurality of separate looped endless bands in a nested and superimposed relation. The patent states that the bands are free to move relative to each other even though the spacing between adjacent bands is relatively small. These bands are formed in an apparatus comprising two rigid metallic anode plates. The metallic surface of the cylindrical mandrel is a cathode. By rotating the mandrel and at the same time interconnecting the cathode and anodes to the electrical power supply, material in the electrolyte bath is plated onto the surface to form a continuous or endless annular band.
During the above process, the belt is regularly removed from the electrolyte bath in order to coat it with a copper coating solution which keeps the belts from adhering to one another. Otherwise one very thick belt would be formed, instead of the several thin belts which are required, and it is the multiple layers of thin belts that are most advantageous for the operation of the continuously variable transmission. However, this removal step necessitates additional handling of the material and increases the number of steps and the expense of achieving the final product.
Thus, while the prior art has disclosed the use of the electroforming process for the manufacture of endless metal belts, it has failed to disclose a simple, inexpensive method for providing a multilayer endless metal belt which has the uniform small gaps, the exacting tolerances and the necessary low adhesion between layers required for the belts to slip easily over each other.
Endless metal belts have been taught in the prior art for many purposes, including use with continuously variable transmissions.
U.S. Pat. No. 3,604,283 to Van Doorne discloses a continuously-variable transmission. The driving mechanism comprises a driving pulley with a V-shaped circumferential groove, a driven pulley with a V-shaped circumferential groove, and a flexible endless member having chamfered (beveled) flanks interconnecting and spanning the pulleys. The diameters of the pulleys automatically and steplessly can be varied with regard to each other in such a way that an infinite number of different transmission ratios can be obtained. The described driving member is a flexible endless member consisting of one or more layers of steel belts.
U.S. Pat. No. 4,661,089 to Cuypers discloses an endless metal belt for use with a continuously variable transmission which can be subjected to greater strains and which has considerably longer service life. This patent describes an endless metal belt wherein the tensile stresses during operation are decreased by compressive stresses at the belt's edge zone. When such stresses are reduced, in particular by the tensile stresses caused by the bending stress, the strain on the belts is reduced and the likelihood of belt breakage caused by hairline cracks occurring from the edges is decreased.
In view of the great demand and many uses for endless metal belts, it is very desirable to find a less costly method of manufacturing these belts, and in such a manner that they will have the exacting tolerances needed.